Effect of process parameters and composition on mechanical, thermal, and morphological properties of polypropylene/sawdust composites

Abstract

Polypropylene/sawdust composites have been prepared according to a statistical experimental design, with varying sawdust and compatibilizer (maleic anhydride grafted PP) concentrations. To investigate process conditions, composites were first extruded in a twin screw extruder coupled to a Haake torque rheometer, without degassing, and then reextruded in a Werner Pfleiderer twin screw extruder, with two degassing zones. Process conditions were analyzed according to statistical techniques. Effect of the variables on mechanical properties was assessed through flexural modulus, tensile strength, and percent elongation at break and morphology was assessed by scanning electron microscopy. Comparison between the extruded and reextruded compounds indicated the need to reduce moisture, prior to and during processing, as well as the need of effective mixing of the compounds. Sawdust concentration showed to be the variable which affected most all properties assessed. Increase in sawdust concentration resulted in increased composite stiffness. The presence of the compatibilizer caused a slight increase in tensile strength and reduction in percent elongation at break, indicating improved adhesion at the PP/ sawdust interface. The reprocessed compounds were also analyzed by differential scanning calorimetry. © 2008 Wiley Periodicals, Inc.